The present invention generally relate to control mechanisms, and more particularly relates to electro-hydraulic pressure control mechanisms having integral pressure sensors.
Modern hydraulic or electrohydraulic brake systems for motor vehicles are equipped with electronically controlled devices for controlling the hydraulics (control mechanisms). The electronic control devices permit the adjustment of brake force at the wheels by pressure increase or reduction in the hydraulic lines that lead to the brake cylinders in dependence on sensors for the purpose of measuring the driving condition.
On the one hand, there are known control mechanisms with a control for avoiding or reducing undesirable wheel slip (e.g. ABS) as well as extended more complex systems for driving dynamics control which are able to actively build up brake pressure at determined wheels in critical driving situations (ESP, TCS). In the course of the general miniaturization and cost reduction, the above-mentioned control mechanisms for brakes have become smaller and compacter in recent times.
Control mechanisms (integrated controllers) of this type are basically comprised of two function blocks: a hydraulic control unit (valve block, HCU) with the hydraulic valves and an electronic unit (ECU) that comprises the overall electronic system such as electromagnetic coils, power semiconductors, and microcontrollers. Depending on the operating mode of the brake, the hydraulic pressure buildup occurs either in the master cylinder that is connected to a brake pedal, or by means of a pump motor which is arranged on the side opposite the electronic controller.
As stated above, the control mechanisms comprise two housing units being assembled during manufacture. The electronic controller comprises the total electronic system of the control mechanism such as electromagnetic coils for actuating the valves, electrical contacts, power semiconductors and microcontrollers, generally, on one single circuit board. Once the controller housing and the valve block are assembled, the valve coils and the valves reside in close proximity and all necessary electrical contacts are made between the valve block and the printed circuit board (principle of the magnetic plug).
In some design variants the electric feed lines, by way of a rod-shaped motor plug, are passed through a bore in the hydraulic part of the control mechanism. The latter motor plug projects from the hydraulic block when the magnetic plug is assembled, so that contacting of the hydraulic motor can also occur during the assembly of the magnetic plug.
It has shown that additional pressure information is required from the hydraulic part of the control mechanism to meet the various control tasks existing in more recent improved brake control mechanisms. This applies equally to current electronic brake systems with a purely hydraulic transmission of the brake pressure as well as for future brake systems wherein the required brake force is generally transmitted to the brake actuators (e.g. control mechanism with pressure accumulator) in an electric way (electrohydraulic brake (EHB) or brake systems with active hydraulic brake force assistance (OHBV (OHBxe2x80x94Optimized Hydraulic Brake)).
In conventional hydraulic brake systems on which the present invention is based, it is known to measure the pressure of the hydraulic fluid outside the integrated control mechanism, e.g. in the area of the tandem master cylinder (TMC). It is usual that the pressure sensor is connected to the tandem master cylinder by a screw coupling for this purpose.
An object of the present invention is to disclose a braking device which, compared to prior art braking devices, is equipped with an apparatus for pressure measurement without departing from the objective of achieving a compact type of construction and low-cost manufacture. The most important aspect in this respect is the constructive extension of the functionality of an already existing highly integrated control mechanism by exploiting a small mounting space available.
This object is achieved by the device comprising an assembled control mechanism wherein a first plug-in housing unit essentially containing the electronic components on one or more component carriers, is plugged together with a block-shaped solid part at a first surface of the solid part for establishing a magnetic and electrical connection, with said solid part including magnetically operated hydraulic valves for the actuation of the brakes and hydraulic lines, and with said device comprising pressure sensors for measuring the pressure in the hydraulic lines at appropriate measuring points, wherein the pressure sensor(s) is/are integrated in the assembled control mechanism.
The present invention discloses a device which permits achieving a more straightforward, more robust, less expensive and also reliable connection of pressure sensors to the hydraulic unit and, in addition, provides a possibility of tolerance compensation during the assembly of the controller housing and the valve block, as will be described in detail in the following.
According to the solution illustrated in FIGS. 1 to 6, the pressure sensor 19 is mechanically and hydraulically coupled to the valve block 12 by way of a bore in the valve block, e.g. by means of a clinched engagement. On a side of the pressure sensor facing the housing of the electronic controller 11, the said sensor has an electrical contact with spring elements in order to provide a slidable contact after the valve block and the controller have been joined. After the controller and the valve block have been assembled, the pressure sensor passes through the controller housing and, thus, is completely integrated in the control mechanism (FIGS. 2, 5, and 6).
During manufacture of the control mechanism, the pressure sensor and the pump motor are mounted on the valve block 12 before the controller and the valve block are joined. The problem encountered in manufacture with respect to the general manufacturing tolerances that have to be taken into consideration is that the position of the pressure sensor, especially the position of the bore provided for this in the valve block is generally determined already prior to the plug-in operation of controller and valve block. In addition, it must be taken into account that during the plug-in action according to the embodiment illustrated in FIG. 6, the electrical contact of the pump motorxe2x80x94apart from the electrical contact of the pressure sensorxe2x80x94is established by way of a rod-shaped motor adapter 9 that projects from the valve block. It is important that all male elements of the electric plugs will exactly mate with the plug""s female elements during the plug-in action. However, this is not easy to fulfill for the pressure sensor contacts 13 and the motor contacts due to the existing tolerances. When first the rod-shaped motor plug engages a mating tubular guide in the controller housing in the assembly operation of controller housing and valve block, the relative positioning of the controller housing and the valve block is defined by the position of the motor plug. Due to this fixation, existing tolerances cause the plug contacts of the sensor to have a position that is not accurately determined.
The above-mentioned tolerances, which occur in each case in the assembly of the controller housing accommodating the electronics and the hydraulic valve block, may accumulate locally in an unfavorable way, especially during the step of assembling the valve block and the controller housing. Contacting of an actuator or sensor arranged on the hydraulic block with the printed circuit board in the controller housing, with the plug mechanism maintained, is impaired or prevented due to the tolerances developing.
In a favorable embodiment of the present invention, the above problem is solved by providing a contact zone between the sensor and the printed circuit board, with said zone rendering it possible to compensate tolerances by using slidable contact elements. These elements may e.g. be springs or bushes displaceable in recesses. Advantageously, this permits broadening the tolerance limits in preceding steps of manufacture. The indicated contact zones allow tolerance compensation perpendicular to the surface 17 of the valve block and in parallel thereto. In addition, tolerance compensation allowing a rotation about the longitudinal axis of the pressure sensor to a certain extent is favorably provided.
In another favorable embodiment, the pressure sensor is structurally united with the motor contacting element in order to overcome the problem of tolerances. The advantage of combining the electrical contacts of the pressure sensor(s) involves a more reliable electrical contacting and, in addition, a simplified manufacture.
Besides, the plug-in housing unit with the electronic components permits greater ease of packing and transport. This construction is advantageous, among other things, because it obviates the need for an adapter guide 10, 32 (see FIGS. 2 and 6) provided in per se known electronic housing units.
Still another favorable embodiment discloses an improved seal-tightness of the pressure sensor with respect to moisture, likewise permitting tolerance compensation in the described fashion.
The advantage of integrating the pressure sensor into the brake control mechanism according to the invention is that the pressure sensor is also encompassed by the housing of the electronic controller so that it is protected against environmental influences to a much better degree than a pressure sensor that is arranged externally, e.g. on the tandem master cylinder. Another advantage is that the integration of one or more pressure sensors in the control mechanism renders additional cable harnesses unnecessary.